/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

/**
 * @author Alexander Y. Kleymenov
 */

package org.apache.harmony.luni.util;

import java.io.UnsupportedEncodingException;

/**
 * This class implements Base64 encoding/decoding functionality as specified in
 * RFC 2045 (http://www.ietf.org/rfc/rfc2045.txt).
 */
public class Base64 {

	private static final byte[] map = new byte[] { 'A', 'B', 'C', 'D', 'E',
			'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R',
			'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e',
			'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
			's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4',
			'5', '6', '7', '8', '9', '+', '/' };

	public static byte[] decode(byte[] in) {
		return decode(in, in.length);
	}

	public static byte[] decode(byte[] in, int len) {
		// approximate output length
		final int length = len / 4 * 3;
		// return an empty array on emtpy or short input without padding
		if (length == 0) {
			return new byte[0];
		}
		// temporary array
		final byte[] out = new byte[length];
		// number of padding characters ('=')
		int pad = 0;
		byte chr;
		// compute the number of the padding characters
		// and adjust the length of the input
		for (;; len--) {
			chr = in[len - 1];
			// skip the neutral characters
			if ((chr == '\n') || (chr == '\r') || (chr == ' ') || (chr == '\t')) {
				continue;
			}
			if (chr == '=') {
				pad++;
			} else {
				break;
			}
		}
		// index in the output array
		int out_index = 0;
		// index in the input array
		int in_index = 0;
		// holds the value of the input character
		int bits = 0;
		// holds the value of the input quantum
		int quantum = 0;
		for (int i = 0; i < len; i++) {
			chr = in[i];
			// skip the neutral characters
			if ((chr == '\n') || (chr == '\r') || (chr == ' ') || (chr == '\t')) {
				continue;
			}
			if ((chr >= 'A') && (chr <= 'Z')) {
				// char ASCII value
				// A 65 0
				// Z 90 25 (ASCII - 65)
				bits = chr - 65;
			} else if ((chr >= 'a') && (chr <= 'z')) {
				// char ASCII value
				// a 97 26
				// z 122 51 (ASCII - 71)
				bits = chr - 71;
			} else if ((chr >= '0') && (chr <= '9')) {
				// char ASCII value
				// 0 48 52
				// 9 57 61 (ASCII + 4)
				bits = chr + 4;
			} else if (chr == '+') {
				bits = 62;
			} else if (chr == '/') {
				bits = 63;
			} else {
				return null;
			}
			// append the value to the quantum
			quantum = (quantum << 6) | (byte) bits;
			if (in_index % 4 == 3) {
				// 4 characters were read, so make the output:
				out[out_index++] = (byte) ((quantum & 0x00FF0000) >> 16);
				out[out_index++] = (byte) ((quantum & 0x0000FF00) >> 8);
				out[out_index++] = (byte) (quantum & 0x000000FF);
			}
			in_index++;
		}
		if (pad > 0) {
			// adjust the quantum value according to the padding
			quantum = quantum << (6 * pad);
			// make output
			out[out_index++] = (byte) ((quantum & 0x00FF0000) >> 16);
			if (pad == 1) {
				out[out_index++] = (byte) ((quantum & 0x0000FF00) >> 8);
			}
		}
		// create the resulting array
		final byte[] result = new byte[out_index];
		System.arraycopy(out, 0, result, 0, out_index);
		return result;
	}

	public static String encode(byte[] in, String charsetName)
			throws UnsupportedEncodingException {
		int length = in.length * 4 / 3;
		length += length / 76 + 3; // for crlr
		final byte[] out = new byte[length];
		int index = 0, i, crlr = 0;
		final int end = in.length - in.length % 3;
		for (i = 0; i < end; i += 3) {
			out[index++] = map[(in[i] & 0xff) >> 2];
			out[index++] = map[((in[i] & 0x03) << 4)
					| ((in[i + 1] & 0xff) >> 4)];
			out[index++] = map[((in[i + 1] & 0x0f) << 2)
					| ((in[i + 2] & 0xff) >> 6)];
			out[index++] = map[(in[i + 2] & 0x3f)];
			if (((index - crlr) % 76 == 0) && (index != 0)) {
				out[index++] = '\n';
				crlr++;
				// out[index++] = '\r';
				// crlr++;
			}
		}
		switch (in.length % 3) {
		case 1:
			out[index++] = map[(in[end] & 0xff) >> 2];
			out[index++] = map[(in[end] & 0x03) << 4];
			out[index++] = '=';
			out[index++] = '=';
			break;
		case 2:
			out[index++] = map[(in[end] & 0xff) >> 2];
			out[index++] = map[((in[end] & 0x03) << 4)
					| ((in[end + 1] & 0xff) >> 4)];
			out[index++] = map[((in[end + 1] & 0x0f) << 2)];
			out[index++] = '=';
			break;
		}
		return new String(out, 0, index, charsetName);
	}
}
